The NX is a starter ship. Everyone is high enough for that. You need an open shipslot, yeah. You should have at least two of those ( unless this is a silver restriction)
How did you buy it?
Were you in game with your character or did you buy it from the website store?
If the second one you need to open the C-Store in game and claim it for your character.

Yeah I just saw that. It kind of blows. They should at least warn you before you buy. What I really need are some better weapons ATM. All I have a dual torpedo upgrade and that has a 45 second respawn time if I've got torpedoes to launch. I accepted a diplomatic mission were I must gather dilithium and deliver it back to another Starfleet vessel. It's impossible, because somehow the big heavy cruisers see me and they attack us both and NONE of my phaser banks or photon torpedoes does a damn thing to them.